Interpretive Summary: Limited information is available on the effects of irrigated crop management practices on nitrous oxide (N2O) emissions. Therefore, N2O emissions from several irrigated cropping systems receiving N fertilizer rates ranging from 0 to 246 kg N ha-1 were monitored during the 2005 and 2006 growing seasons. Cropping systems included: conventional-till (CT) continuous corn (CC) (CT-CC); no-till (NT) CC (NT-CC); NT corn-dry bean (NT-CDb); and NT corn-barley (NT-CB). In 2005, half the N was applied as urea-ammonium nitrate (UAN) at planting to all corn plots with the rest of the N applied as ESN®, a polymer-coated urea (PCU), in mid-June. The entire N rate was applied as UAN at barley and dry bean planting in the NT-CB and NT-CDb plots in 2005. All plots were in corn in 2006, with PCU applied at half the N rate at corn emergence and half as dry urea in mid-June, both banded on the soil surface in the corn row followed by irrigation. N2O fluxes were measured 2 to 3 times each week during the growing season. Linear increases in N2O emissions were observed with increasing N-fertilizer rates, but emission amounts varied with growing season. Growing season N2O emissions were greater from the NT-CDb system during the corn phase of the rotation than from the other cropping systems. Crop rotation and N rate had more effect than tillage system on N2O emissions. N2O emissions from N application ranged from 0.30 to 0.75% of N applied. Spikes in N2O emissions following N fertilizer application were greater with UAN and urea than with PCU fertilizer. The PCU showed potential for reducing N2O emissions from irrigated cropping systems. These results can be used by model developers to verify projected N2O emissions from environmental models for irrigated crop production systems.

Technical Abstract:
This study evaluated the effects of irrigated crop management practices on nitrous oxide (N2O) emissions. Emissions were monitored from several irrigated cropping systems receiving N fertilizer rates ranging from 0 to 246 kg N ha-1 during the 2005 and 2006 growing seasons. Cropping systems included: conventional-till (CT) continuous corn (Zea mays L.) (CC) (CT-CC); no-till (NT) CC (NT-CC); NT corn-dry bean (Phaseolus vulgaris L.) (NT-CDb); and NT corn-barley (Hordeum distichon L.) (NT-CB). In 2005, half the N was subsurface band applied as urea-ammonium nitrate (UAN) at planting to all corn plots with the rest of the N applied surface broadcast as ESN®, a polymer-coated urea (PCU), in mid-June. The entire N rate was applied as UAN at barley and dry bean planting in the NT-CB and NT-CDb plots in 2005. All plots were in corn in 2006, with PCU being applied at half the N rate at corn emergence and a 2nd N application as dry urea in mid-June, both banded on the soil surface in the corn row followed by irrigation. N2O fluxes were measured during the growing season using static, vented chambers, one to three times per week, and a gas chromatograph analyzer. Linear increases in N2O emissions were observed with increasing N-fertilizer rate, but emission amounts varied with growing season. Growing season N2O emissions were greater from the NT-CDb system during the corn phase of the rotation than from the other cropping systems. Crop rotation and N rate had more effect than tillage system on N2O emissions. N2O emissions from N application ranged from 0.30 to 0.75% of N applied. Spikes in N2O emissions following N fertilizer application were greater with UAN and urea than with PCU fertilizer. The PCU showed potential for reducing N2O emissions from irrigated cropping systems. [GRACENet Pubication].